Magnesium halide is a key component of titanium based Ziegler-Natta catalysts which have been used extensively in the polyolefin industry over the past 50 years. These catalysts are typically composed of titanium incorporated onto the surface of a magnesium halide support. It has been recognized that the catalyst properties depend heavily on the chemical and physical properties of magnesium halide support and the support properties influence the morphology of the resulting polymer. Consequently, there has been intense effort directed to preparing active magnesium halide supports for olefin polymerization catalysts.
Most of the methods known in the art for preparing such magnesium halide supports utilize various electron donating solvents such as alcohol, ester, siloxy, and ether compounds. For example, U.S. Pat. Nos. 4,987,212 and 4,642,328 discloses methods involving the reaction of R2Mg solution with an alkylhalide in a mixed solvent of ether and heptane. U.S. Pat. Nos. 5,091,353 and 5,192,732 describe a method wherein magnesium halide containing aluminum is precipitated from an alcohol solution of magnesium halide by the addition of alkylaluminum compounds to the solution. In a method described in U.S. Pat. No. 4,302,566, THF is mixed with magnesium halide and titanium halide compounds to make a solution from which a solid catalyst component is prepared by re-precipitation.
Method for preparing a magnesium halide support that utilize electron donating solvents suffer the drawback that excessive amounts of the electron donating solvent can intercalate into the matrix of the support and ‘poison’ the catalyst. As a result, it is often necessary to extensively wash the matrix with non-polar solvents or to treat the matrix with strong Lewis acids to remove excessive electron donating solvent. These steps lengthen the preparation process and themselves can potentially contaminate or poison the catalyst.
U.S. Pat. No. 4,478,221 and European Patent No. 0 703 246 A1 describe a method that does not utilize an electron donating solvent, wherein magnesium metal powder is reacted with butylchloride in a non-polar solvent in the presence of Ti(OR)4 to initiate the reaction and then further treatment with TiCl4/Ti(OR)4/butylchloride results in a magnesium halide supported catalyst. According to this method, the active titanium catalyst is formed concomitantly with the precipitation of the magnesium halide support. This makes it difficult to control the homogeneity of the active site, therefore, polymers synthesized using these catalysts display broad molecular distributions. Also, the catalytic amount of Ti(OR)4 used to initiate the reaction between magnesium powder and butylchloride results in a tiny amount of Ti(OR)4-formed active site within the magnesium halide support itself. This active site displays formidable activity and competes with the desired active catalyst, producing heterogeneous polymers. It is therefore difficult to employ a magnesium halide support formed in this manner as a support for olefin polymerization.
The reaction between magnesium and alkylhalide is seldom successful without using titanium compounds such as TiCl4 or Ti(OR)4 to initiate the reaction. It would be beneficial to develop a new method to initiate the reaction between magnesium and alkyl halide without using titanium compounds.
U.S. Pat. No. 5,990,034 describes a method wherein a mixture of alkylaluminum and alkylmagnesium is reacted with chlorosilane containing a Si—H bond to produce a magnesium halide support without using an ether solvent. However, alkylmagnesium compounds are expensive, so this method for preparing a magnesium halide support is not cost effective.